Micropuncture studies directed at elucidation of the physiology and pathophysiology of kidney function in several areas will be continued. Specific projects include experiments to identify and define the renal and individual nephron mechanisms involved in the initial phase of hypertension when arterial blood pressure rises rapidly in 5 to 8 week old spontaneously hypertensive rats. Control studies will be done in WKY animals. Studies will continue on two models of acute renal failure: that following 1 hour of renal artery occlusion and that produced by feeding animals a high urate diet supplemented by oxonic acid. Studies on the latter model will be directed primarily towards determining the permeability of the tubular epithelium to large molecules in the acute obstructive phase of the condition. Studies in the ischemia model will be directed primarily at following the disturbance in excretory function in the recovery phase and determining the effects of several experimental interventions on its course. Acute unilaterial denervation in volume expanded rats produces a further marked increase in urine flow from the denervated kidney which is accompanied by a decrease in salt and water excretion by the contralateral innervated kidney. Both occur without a change in GFR or renal blood flow and result from reciprocal changes in the rate of tubular reabsorption. Experiments will be performed to ascertain if the increased reabsorption in the innervated kidney under this condition results from increased neural activity to the kidney just as the decrease in reabsorption results from decreased neural activity subsequent to denervation. BIBLIOGRAPHIC REFERENCES: Effect of renal sympathetic nerve stimulation on proximal water and sodium reabsorption. E. Bello-Reuss, D.T. Trevino and C.W. Gottschalk. J. Clin. Invest. 57: 1104-1107, 1976. Acute unilateral renal denervation in rats with extracellular volume expansion. E. Bello-Reuss, E. Pastoriza-Munoz, and R.E. Colindres. Am. J. Physiol. 232: F26-F32, 1977.